I believe that bitcoin will plateau at $5000 or above within 20 years. It may someday go much higher, but I believe that is decades away. So I think that it is safe to buy at any price below $5000 as long as you are willing to buy and hold. If you plan on selling soon then this is probably not a safe time to buy. I would not be surprised if the price falls below $300 once or twice more on its way to $5000+
We are close to 300$ so we may go back there a few times but your 5000$ goal is a bit arbitroray : why not 3,500$ or 11,000$; we don't know what will be the value of the USD in 10 years except that it will be a lot less than now; maybe 50% less but maybe 98% less
